1. Field of Invention
The present invention relates to a control circuit and a control method thereof. More particularly, the present invention relates to a control circuit for reducing current error in an output of a power converter and a control method thereof.
2. Description of Related Art
In a conventional switching power supply or a light-emitting diode (LED) driver, if there is no additional control for the output current, it is difficult to achieve a fixed output current within a wide range of input voltage, such as 90˜270 AC voltage.
As shown in FIG. 1, in order to reduce the cost of circuitry, a conventional power converter 100 typically uses a primary side 101 of a transformer to control the output current. The inductor current in the primary side 101 is usually compared with an error signal for determining a cut-off point of a power switch 102. However, in practice, an error in the inductor current is caused easily due to the effect of the propagation delay of the circuitry in the power converter 100, thereby resulting in an inaccurate cut-off point of the power switch 102 and a variation in the output voltage and current, ultimately degrading the line regulation of the power converter 100. For example, as shown in FIG. 2, in an inductor current waveform 201, the real peak value of the inductor current should be Ipeak1. However, due to the effect of the propagation delay Td of the circuitry, the actual peak value becomes Ipeak. Further, when the input voltage increases or there is an error in the amount of the inductance, the inductor current changes to the waveform 202, and thus the real peak current is changed to Ipeak2 from Ipeak1. In each of the waveform 201 and the waveform 202, error caused by the propagation delay Td varies the output current and degrades the line regulation.